A conventional micro-mechanical optical switch is described, for example, in Photonics Technology Letters, vol. 10, pp. 525-527, April, 1998. An optical switch described in this publication includes input optical fibers disposed along one side of a rectangular substrate, output optical fibers disposed along the crossing side, and movable mirrors arranged in a matrix on the substrate. The movable mirrors further include actuators that convert electric energy into mechanical actions.
Each of the movable mirrors reflects light toward determined direction. Therefore, required number of the movable mirrors is product between the number of input ports and output ports.
In general, the number of the mirrors in a single substrate is limited to around 2500, because cubic content of the actuator is larger than the mirror. When numbers of the input ports and the output ports are equal, those numbers are respectively limited to around 50.